2026-09-19T01:46:19Zhttps://dspace.mit.edu/server/oai/request

oai:dspace.mit.edu:1721.1/447692022-01-13T07:54:37Zcom_1721.1_7582com_1721.1_7581col_1721.1_131023

Sidney Yip. Monasterio Velásquez, Paul Rene Massachusetts Institute of Technology. Dept. of Nuclear Science and Engineering. Massachusetts Institute of Technology. Department of Nuclear Science and Engineering 2009-03-16T19:40:41Z 2009-03-16T19:40:41Z 2008 http://hdl.handle.net/1721.1/44769 300276757 Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2008. "May 2008." Includes bibliographical references (p. 60-62). As part of a multi-scale approach for modeling hydrogen embrittlement in hardened steels we have investigated, employing density functional theory methods, the stability and concentrations of the point defect clusters present in metastable Fe-C-H alloys with vacancies. The defect spectrum is found to be strongly dependent on the local vacancy concentration, and for low hydrogen levels sharp highly non-linear changes in the defect cluster population are observed at critical vacancy concentrations. This critical-like behavior suggests an energy activation mechanism which can be characterized by an effective defect-cluster formation energy barrier. By analogy with similar activated processes such as the liquid-to-glass transition in super-cooled liquids, we postulate that this criticality is associated with the presence of deep wells in the energy landscape where chemical composition plays the role of generalized coordinate. Increases in the hydrogen content have the qualitative effect of reducing the slopes in the defect concentrations. The drastic sensitivity of the defect cluster spectrum to local changes in vacancy and impurity concentrations implies that in proximity of surfaces and extended defects multiple defect clusters become statistically significant and migration dependent phenomena, such as creep-relevant to hydrogen embrittlement-and super-diffusion, should be controlled by multiple activation barriers. by Paul Rene Monasterio Velásquez. S.M. 62 p. eng Massachusetts Institute of Technology M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission. http://dspace.mit.edu/handle/1721.1/7582 Nuclear Science and Engineering. Hydrogen effects on the point defect spectrum in Fe-C alloys Thesis application/pdf false Publication unknown unknown <Publication xmlns="https://www.openaire.eu/cerif-profile/1.1/" id="2d1911cc-892a-457b-8913-99d6b13ac0e8"> <Type xmlns="https://www.openaire.eu/cerif-profile/vocab/COAR_Publication_Types">http://purl.org/coar/resource_type/c_1843</Type> <Language>eng</Language> <Title>Hydrogen effects on the point defect spectrum in Fe-C alloys</Title> <PublishedIn> <Publication> </Publication> </PublishedIn> <PublicationDate>2008</PublicationDate> <Authors> <Author> <DisplayName>Monasterio Velásquez, Paul Rene</DisplayName> <Affiliation> <OrgUnit> </OrgUnit> </Affiliation> </Author> </Authors> <Editors> </Editors> <Publishers> <Publisher> <DisplayName>Massachusetts Institute of Technology</DisplayName> <OrgUnit /> </Publisher> </Publishers> <License>http://dspace.mit.edu/handle/1721.1/7582</License> <Keyword>Nuclear Science and Engineering.</Keyword> <Abstract>As part of a multi-scale approach for modeling hydrogen embrittlement in hardened steels we have investigated, employing density functional theory methods, the stability and concentrations of the point defect clusters present in metastable Fe-C-H alloys with vacancies. The defect spectrum is found to be strongly dependent on the local vacancy concentration, and for low hydrogen levels sharp highly non-linear changes in the defect cluster population are observed at critical vacancy concentrations. This critical-like behavior suggests an energy activation mechanism which can be characterized by an effective defect-cluster formation energy barrier. By analogy with similar activated processes such as the liquid-to-glass transition in super-cooled liquids, we postulate that this criticality is associated with the presence of deep wells in the energy landscape where chemical composition plays the role of generalized coordinate. Increases in the hydrogen content have the qualitative effect of reducing the slopes in the defect concentrations. The drastic sensitivity of the defect cluster spectrum to local changes in vacancy and impurity concentrations implies that in proximity of surfaces and extended defects multiple defect clusters become statistically significant and migration dependent phenomena, such as creep-relevant to hydrogen embrittlement-and super-diffusion, should be controlled by multiple activation barriers.</Abstract> <Access xmlns="http://purl.org/coar/access_right" > </Access> </Publication>